Continuous, accurate measurement of core-body temperature is an important tool in monitoring the well-being of a patient. Traditionally, core-body temperature has been measured using invasive devices, such as probes in the esophagus placed close to the heart or probes in the bladder inserted via the urinary tract. Such probes are generally unsuitable for monitoring patients not under anesthesia. Therefore, various non-invasive sensing devices have been developed, which estimate and output the core-body temperature based on body-surface measurements. Devices of this sort are described, for example, in U.S. Pat. No. 7,625,117 and in U.S. Patent Application Publication 2009/0299682, whose disclosures are incorporated herein by reference.
Many vital signs monitors include a standard plug for connecting to a thermistor-based temperature probe. Probes of this type were originally developed and standardized by YSI Inc. and include the YSI 400 and YSI 700 types. Such probes include a thermistor sensor, with a calibrated temperature response, and a cable with a standard connector for plugging into the monitor. The vital signs monitor simply measures the resistance value across the output connector of the cable. The monitor calculates and displays the temperature according to the measured resistance and the known calibration curve.
U.S. Pat. No. 7,641,390, whose disclosure is incorporated herein by reference, describes a method for digitally controlling the resistive output of a temperature probe. The method uses a temperature sensor, a processor and a means under the control of the processor for modifying the resistive output, such as a digital potentiometer. In one embodiment, the processor reads the temperature sensor and adjusts the potentiometer based on a correlative or predictive technique so as to provide a modified output that matches that of a standard resistive temperature probe and is compatible for display on a multi-parameter monitor.